1. Field of the Invention
The present invention relates generally to substrate surface processing apparatus and more particularly to a removable shutter mechanism for use in closing the substrate exposure aperture of a semiconductor processing or other deposition or etching process chamber.
2. Brief Description of the Prior Art
It is a common practice in the semiconductor processing industry to plate the surface of a semiconductor wafer with a metal or metal oxide using a sputtering technique wherein a wafer is disposed in an evacuated chamber and a metallic material is electrically removed from an anode and plated onto the wafer surface.
Wafers are normally shuttled in and out of the processing chamber by a robotic mechanism. The conventional practice is to either interrupt the plating process each time a wafer is inserted or removed from the processing chamber, or in the case where the sputtering operation is continuous, to provide a shuttering mechanism of some type for covering the opening normally occupied by the wafer.
In the first case, the primary disadvantage relates to the reduced throughput of the system, as time must be allowed for ramping up and ramping down the plating operation.
Apparatus for implementing the second case is illustrated in FIG. 1 of the drawing and includes an evacuable chamber formed by a housing 10 and closure 12, the lower surface of the closure being formed by a metallic plate 14 which serves as the system anode. Also depicted is a source of material to be sputtered onto a wafer 16 shown supported above a heating plate 17 by a lift assembly 18 including four upstanding fingers 19. The system cathode is formed by a bowl 20 having a central aperture 22 formed therein. Resting within the bottom of bowl 20 is an annular clamping mechanism 24 having a lip 26 formed about an inner annulus thereof and adapted to be engaged by the perimeter of wafer 16 as it is raised by lift assembly 18 into the plating position shown by the dashed lines 16'. The heating plate 17 is movable between the lower position shown by the solid lines and an upper position immediately beneath wafer 16' as depicted by the dashed lines 19'.
In order to close the plating aperture 22 during the removal and replacement of wafer 16, a shutter 32, normally positioned to the side, is moved into the position shown by the dashed lines 32' so as to block the path of the plating ions. Since plating material will build up on the surfaces of both shutter 32, cathode 20 and clamping ring 24, shutter 32 must be positioned above these elements a sufficient distance to prevent contact therewith. Accordingly, in order to be effective the shutter 32 must be much larger than a wafer. This means that the inner peripheral surface portion of the clamping mechanism covered by the shutter can not be reconditioned during the time that the shutter is in position. Accordingly, the chamber must be periodically opened to allow access to the clamp.
Furthermore, where a reactive gas is introduced into the chamber to react with the metal ions and form metal oxides, the oxides that plate onto the shutter will be somewhat brittle and unless removed will crack and flake off causing contamination of the chamber. Accordingly, a particular shutter can only be used for a limited time after which the chamber must be opened to allow its replacement. This of course limits the efficiency of the apparatus and affects the reliability of the system.
Similar apparatus is used to implement etching and other deposition processes and is subject to the same or similar disadvantages pointed out above.